The instant invention relates to the regulation of a drawing frame of the textile industry in which drafting of a fiber sliver can be modified in a controlled and/or regulated manner. The concept of regulation includes, in this case, control and/or regulation of drafting. The regulation is designed to correct environmental influences and internal machine influences so that the errors in drafting caused by these influences are compensated for. The development of regulating systems for the drafting of a fiber sliver has produced a great number of specialized controls and regulating systems according to the state of the art, and most of these are designed to handle individual, specialized problems in the overall picture of a regulating system.
Each of these regulating systems of a drawing frame is based on the formulation of a process model, as well as on the observation and evaluation of the reactions of the drawing frame to the control magnitudes so as to finally optimize the transmission characteristic of the regulator (see also EP 412 448).
In this context, the regulating algorithm describes the relationship between the control magnitudes involved. This method is very effective if the relationship between the magnitudes is simple, i.e. easy to formulate, and if it is sufficiently well known. The latter is difficult for the simulation of technical processes such as the regulation of a drawing frame because of the complexity of factors influencing the process. Such influence factors, which so far have been impossible to reliably compensate for, are for example:
the temperature on the scanning roller PA1 the humidity on the fiber sliver PA1 stoppage time of the fiber sliver between the scanning rollers PA1 standing time of feeding cans filled with fiber slivers PA1 Temperature: PA1 Temperature of the scanning roller PA1 Air humidity in the environment of the fiber sliver PA1 Stoppage time of the fiber sliver between the scanning rollers PA1 Standing time of feeding cans filled with fiber slivers PA1 Material properties of the fiber sliver; and PA1 Output speed of the drawing frame.
Efforts to optimize the regulation algorithm are in practice facing increasing problems of redundancy of measured values or with the stability of the regulating circuit.
Some of these influence factors are briefly discussed below:
For the scanning rollers sensing fiber thickness, the determining temperature after machine start-up is the environmental temperature. After start-up, the temperature of the scanning roller changes.
Friction against the fiber sliver increases the temperature until it reaches operating temperature. The transition in time to operating temperature is more or less rapid, depending on the environmental temperature. This change in temperature (with an unknown time constant) influences the elasticity of the scanning roller and therefore the excursion of the movable roller of the scanning roller, so that the actual measuring result is influenced. This temperature change also influences the sliding or roller friction factors of the scanning roller bearing.
If two identical drawing frames were to be started with the same regulation algorithm in separate production rooms at different environmental temperatures, it would be found that drafting of a fiber sliver is regulated differently during the period of time it would take until a stable operating temperature is reached. This is caused by the influences of different temperature on the elasticity of the movable roller of the scanning roller equipment.
Stoppage times of the machine are time periods during which the fiber sliver is stopped between the scanning rollers. These stoppage times produce changes in fiber sliver thickness due to different lengths of time of being clamped by the scanning rollers.
Standing time of feeding cans filled with fiber slivers is the time from filling of the cans with the slivers until further processing in the drawing frame. If such feeding cans are buffer-stored and are not immediately used for further processing, they are subject to environmental influences (environmental temperature, air humidity). This situation is also described in DE-OS 39 19 284. The properties of the fiber sliver change as a function of the length of time during which temperature and air humidity exert their influence on the sliver.
The sliver's own weight also exerts an influence in that it causes the sliver to be compressed to different degrees as a function of the height to which the can is filled (over a longer period of time).
These various influences lead to measuring errors of the measuring element in drafting, because no conventional mathematical process model exists for the processing and accommodation of magnitudes such as temperature, air humidity, stoppage time, and length of time during which cans remain standing. Regulating systems in a drawing frame, functioning on the basis of such conventional mathematical process models, are insufficiently able to compensate for the above-described influences upon the measuring signals.